1. Field of the Invention
The present invention relates to a serial printer including a platen and a carriage having a printing head secured thereto, and more particularly, to a carriage position control circuit for use in the serial printer for positioning the carriage and the printer.
2. Description of the Related Art
A conventional dot impact serial printer includes a platen and a carriage having a printing head secured thereto. Such a printer is usually provided with an anti-floating device for preventing a printing sheet from being raises from the platen. During printing, the printing sheet is fed by the platen to a first gap between the platen and the carriage and then transferred to a second gap between the platen and the anti-floating device. When printing near the leading edge of the printing sheet, the leading edge is initially positioned close to the head of the carriage. Therefore, the leading edge does not extend to the anti-floating device. As a result, when the serial printer first begins a line feed operation the sheet tends to be raised from the platen since the leading edge of the sheet has not yet reached the anti-floating device.
In order to prevent the sheet from raising in this manner, the carriage is moved to a center position of the platen regardless of the width of the sheet in an effort to maintain the sheet in contact with the platen.
In such conventional serial printer, when the width of the sheet is considerably small as compared to the length of the platen and the sheet is offset to the right or left side of the platen, the centrally positioned carriage is laterally displaced from the sheet. Therefore, the sheet floats away or raises from the platen. If a line feed operation is performed while the sheet is raised from the platen, the sheet will be fed in a skewed manner, a leading edge of the printing sheet will be obstructed by an edge of the anti-floating device or the sheet will be soiled during the printing operation.
In order to solve this problem, there has recently been introduced a serial printer including a non-volatile memory which stores positioning data indicating the proper positioning of the carriage for each size of the printing sheets prior to printing or line feeding. However, the operator must frequently change operating modes of the printer so that appropriate positioning data may be read from the memory in accordance with the paper size of the sheet. Moreover, the use of the printer is restricted to paper sizes that are stored in the memory.